Maintaining roll temperature uniformity in fuser roll systems has long been a concern of printer designers. The temperature along a width of the fuser roll can vary excessively, particularly in systems designed for print media of varying widths, which can adversely affect print quality. Printing long-edge feed paper after printing many copies of short-edge feed paper can also result in decreased printer performance. Using a heat pipe as a fuser roll is a known technique to solve such temperature uniformity issues. However, problems can arise in the complexity in the design of heat pipe fuser rolls, because heat pipes are closed systems and applying heat internally is difficult. Applying heat at one end of the fuser roll can be performed to simplify the geometry of the subsystem, but can result in incident heat flux at the heated end. In low mass, “instant-on” or rapid warm-up fuser roll systems, the low axial conductance of the fuser roll causes a greater thermal non-uniformity than in conventional fusing systems. It is generally preferable in instant-on systems to use a heat pipe with a low volume of fluid such as water or water-alcohol to more rapidly transfer heat from the warmer regions to the cooler regions of the fusing system rolls. Some heat pipe systems incorporate a fiber wicking device to sustain the fluid in the heat pipe. In this minimal fluid configuration, there is a potential for dry-out of the heat pipe evaporator. Systems to pump fluids using more complex interior geometries are also known and used to prevent the evaporator from drying out.
Low energy usage requirements in a fuser roll/pressure roll system can be met by minimizing the thermal mass of the fuser roll. Temperature uniformity can be met by heating element profile and design. Usually, these systems are optimized around the media size and weight most used in the market place. However, various media sizes and weights are used, which can contribute to temperature non-uniformity along the fuser roll axis. Another factor that contributes to temperature non-uniformity is conductive and convective heat losses from the heating lamps and the fuser roll, for example, to the bearings and supporting framework.
U.S. Pat. No. 7,349,660, commonly assigned to Xerox Corporation with the present application and incorporated herein by reference in its entirety, describes a heat pipe in contact with the fuser roll and/or the pressure roll to transfer heat from warmer regions to cooler regions so that a temperature along a length of the fuser roll and/or the pressure roll becomes more uniform.